1. Field of the Invention
The present invention relates to a display material capable of thermal recording and erasure of information such as characters, and a display device utilizing said material.
2. Related Background Art
There are already known reversibly erasable and repeatedly usable information recording materials such as photochromic materials, thermochromic materials, magnetic recording materials etc.
A known display device utilizing thermochromic material employs a display medium of a sandwich structure, composed of a reversible thermochromic material Ag.sub.2 HgI.sub.4 sandwiched between a pair of polyester films. Said display medium is formed as an endless belt positioned over two rollers, and the information is recorded line by line with a thermal head while said medium is displaced. Said material is yellow at normal temperature but becomes yellow-orange at a temperature above 50.degree. C. The color change shows a hysteresis to temperature change, and the material returns to the original color upon cooling. Consequently, in order to retain the recorded information, the display area between the two rollers is maintained at a constant temperature with a panel heater. The recorded information is erased by moving the recording medium away from the display area and by cooling with suitable cooling means. Since such material lacks memory property, the heater has to be turned on continuously. Consequently, the display device is inevitably large and complex, and requires a large electric power consumption. Also the use of a filter may be necessary since the displayed color is not very clear.